(1) Field of the Invention
The invention is related to an aircraft having at least one first and one second engine, each engine comprising a main air inlet opening, a by-pass air inlet opening and a bleed air outlet, said aircraft comprising the features of claim 1.
(2) Description of Related Art
Main air inlet openings of engines in aircrafts and, more particularly, of gas turbine engines in aircrafts, such as e.g. turbo-shaft engines in rotary wing aircrafts, are frequently provided with inlet barrier filter systems comprising air filtration devices that are arranged in the main air paths of the engines for filtering main air streams through the main air inlet openings into the engines. Such inlet barrier filter systems offer a very effective possibility for protecting the engines. However, they are exposed to multiple different operating and background conditions, which may amongst others lead to a clogging of the air filtration devices after a certain time of operation. If this happens during flight operation, a respective power provided by an affected engine could potentially be decreased to an extent where the necessary power to safely continue operation would not be guaranteed any more.
Accordingly, there are strict regulations for certification of inlet barrier filter systems, e.g. especially for so-called CAT A capable helicopters, i.e. helicopters corresponding to the category A definition of the EASA Comment Response Document CRD b.2 Annex I, which may lead to operational limitations for such helicopters. Therefore, already for certification purposes, the inlet barrier filter systems of such helicopters and, more generally, the inlet barrier filter systems on gas turbine engines of aircrafts in general, are provided with by-pass air systems that are adapted to feed the engines with air whenever a clogging of corresponding air filtration devices of the inlet barrier filter systems occurs during flight operation.
In general, a by-pass air system of a gas turbine engine defines a secondary air path of the engine, which is realized without any air filtration device. More specifically, a by-pass air system of a gas turbine engine usually consists of a by-pass air inlet opening that is provided with a by-pass door, which is operable by an associated operating element, i.e. can be opened if required to enable a by-pass air stream through the by-pass air inlet opening into the engine.
The above described by-pass air and main air inlet openings define air intake systems. However, gas turbine engines of aircrafts can also be provided with air outlet systems by means of so-called bleed air outlets for creating an outgoing bleed air stream going out of the engine in operation. Such bleed air outlets are generally arranged downstream of compressor stages of the gas turbine engines, which are upstream of their respective fuel burning sections, so that compressed air, the so-called “bleed air”, can be derived from the gas turbine engines to form the outgoing bleed air stream. This outgoing bleed air stream can advantageously be used e.g. for cross-starting another engine, cabin pressurization, airframe and engine anti-icing, air conditioning and so on.
The document US 2007/0025838 A1 describes an aircraft and, more particularly, a helicopter having a gas turbine engine that is provided with an air induction system. The air induction system is provided with a housing having four openings that comprise primary entryways for receiving air and are located on top and lateral surfaces of the housing. A flat filter panel with a porous filter media is mounted across each opening to define an inlet barrier filter system. The housing further comprises two hollow extensions, each having an opening that, in turn, comprises a by-pass opening for receiving intake air into the housing that supplements or replaces primary intake air received through the flat filter panels. A hinged door covers each by-pass opening and is controllably rotatable by a motorized actuator between a closed position, wherein the by-pass opening is closed, and an open position, wherein intake air may enter the housing through the by-pass opening. The motorized actuator is implemented as an electromechanical actuator.
The document WO 2008/016341 A2 describes an aircraft and, more particularly, a helicopter having a gas turbine engine that is also provided with an air induction system. The air induction system includes a cowling and a filtering unit that is generally enclosed within the cowling. The filtering unit comprises two barrier filter panels with pleated, porous barrier filter elements that are provided with filter media, such as cotton grid fabric, and arranged in a main air intake path for filtering main air streams prior to intake into the engines. The air induction system is further provided with one or more by-pass openings that are covered by associated hinged by-pass doors. Each hinged by-pass door is opened and closed by an actuator that is implemented as an electromechanical actuator.
The document WO 2008/076471 A2 describes an inlet barrier filter system for an aircraft engine, which includes a filter panel with a filter media for filtering a main air stream prior to intake into the engine. The filter panel can be pivoted by means of an associated actuator to form a by-pass air inlet opening, such that air is allowed to bypass the filter panel for streaming via said by-pass air inlet opening into the engine. In other words, the filter panel itself implements the by-pass door of the by-pass air inlet opening. The actuator is implemented as an electromechanical actuator.
The document FR 1 548 724 A1 describes an aircraft and, more particularly, a helicopter having an aircraft engine with an inlet barrier filter system and a by-pass air system. The inlet barrier filter system comprises filter panels for filtering a main air stream prior to intake into the engine and the by-pass air system is provided with by-pass doors that cover associated by-pass air inlet openings. Alternatively, the filter panels can be pivoted to create the by-pass air inlet openings such that air is allowed to bypass the filter panels for streaming via said by-pass air inlet openings into the engine. The filter panels or the by-pass doors can be pivoted by means of associated actuators that are implemented as electrical or hydraulic actuators.
The document US 2013/0092798 A1 describes an aircraft and, more particularly, a helicopter having an aircraft engine that may include a turbine engine, a piston engine, or another type of engine suitable for generating rotation of associated rotor blades, in order to provide thrust for the aircraft. The aircraft engine includes two intakes for receiving air flow for use by the aircraft engine in a combustion process. The helicopter includes two filter systems that are respectively coupled to an associated one of the intakes, such that intake air passes through the filter system prior to entering the air intake of the aircraft engine. Each filter system includes a by-pass closure, which is disposed adjacent to a filter assembly of the filter system. The by-pass closure is movable relative to the filter assembly between a first position, in which the by-pass closure covers and seals the by-pass opening of the filter assembly, and a second position, in which the by-pass closure is spaced apart from the filter assembly. The filter system further includes an actuator for causing relative movement of the by-pass closure between the first and second positions. This actuator may include an electrical actuator, a fluid actuator, a pneumatic actuator or another suitable device.
The document U.S. Pat. No. 3,411,272 describes a helicopter with a turbine engine having an air inlet that is positioned to receive air from an inlet compartment or plenum. The air inlet is provided with a pair of fixed side filter assemblies and a movable top filter assembly. The side filter assemblies are positionally fixed to constantly provide filtering action. The top filter assembly is of a louvered construction including a plurality of fixed louvers and a plurality of pivotably movable louvers having filters, which can be of a conventional construction to capture harmful dirt particles, while passage of air is permitted. The movable louvers cooperate with the stationary louvers in a closed position to completely close the air inlet through an upper portion of the inlet compartment. The movable louvers are pivotally mounted at their lower extremities about associated pivots. Thus, the movable louvers can be pivoted into a position, in which a passage through the top filter assembly is opened, so that air will pass freely there through while bypassing the filters of the louvers. Movement of the movable louvers can be provided by means of an actuator that can be implemented by a pneumatic piston assembly, which can be actuated by a 4-way pneumatic valve, which in turn is actuated by an electric solenoid. The actuation of the solenoid, and hence the pneumatic valve and the movable louvers, is controlled by electrical circuitry.
However, in all of the above-described barrier inlet filter and/or by-pass air systems, a cumulated time of failure detection in the case of a failure of the aircraft engine, or a One Engine Inoperative (OEI)-detection in the case of a failure of an aircraft engine of a multi-engine aircraft, and a subsequent activation of the above described actuators in order to fully open respective by-pass air inlet openings is comparatively long and can take up to six seconds. This applies particularly to electrical and/or electromechanical actuators, which usually further require provision of an associated harness system and additional electrical power supply systems, which makes the construction thereof comparatively complex.
More generally, all of the above-described barrier inlet filter and/or by-pass air systems use actuating systems that are, at least to some extent, electrically operated or activated, so that they require provision of electrical power supply systems. Such electrical power supply systems and the complexity of the respective actuating systems are, however, themselves potential sources of error and failure.
These drawbacks must be considered during construction of aircrafts with respect to flight and operation safety. They must further be considered with respect to certification of inlet barrier filter systems of aircrafts, especially with regard to the strict regulations for helicopters with the above mentioned capability for CAT A operation.
It is, therefore, an object of the present invention to provide an aircraft that comprises at least one first and one second engine, each engine comprising a main air inlet opening, a by-pass air inlet opening and a bleed air outlet, and that overcomes the above described drawbacks.